Consolidated Balance Sheets (Parenthetical) $ in Millions	Mar. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
Statement of Financial Position [Abstract]
Available for sale, at amortized cost	$ 80,959	$ 82,580
Debt Securities, Available-for-sale, Allowance for Credit Loss	176	0
Held to maturity, at Fair Value	12,471	13,005
Debt Securities, Held-to-maturity, Allowance for Credit Loss	45	0
short-term investments amortized cost	3,582	4,291
Reinsurance Recoverable, Allowance for Credit Loss	$ 305	$ 316
Common Shares, shares issued | shares	479,783,864	479,783,864
Common Shares, shares outstanding | shares	451,367,782	451,971,567
Common Shares in treasury, shares | shares	28,416,082	27,812,297